import sys

from google.appengine._internal.django import http
from google.appengine._internal.django.core import signals
from google.appengine._internal.django.utils.encoding import force_unicode
from google.appengine._internal.django.utils.importlib import import_module

class BaseHandler(object):
    # Changes that are always applied to a response (in this order).
    response_fixes = [
        http.fix_location_header,
        http.conditional_content_removal,
        http.fix_IE_for_attach,
        http.fix_IE_for_vary,
    ]

    def __init__(self):
        self._request_middleware = self._view_middleware = self._response_middleware = self._exception_middleware = None

    def load_middleware(self):
        """
        Populate middleware lists from settings.MIDDLEWARE_CLASSES.

        Must be called after the environment is fixed (see __call__).
        """
        from google.appengine._internal.django.conf import settings
        from google.appengine._internal.django.core import exceptions
        self._view_middleware = []
        self._response_middleware = []
        self._exception_middleware = []

        request_middleware = []
        for middleware_path in settings.MIDDLEWARE_CLASSES:
            try:
                dot = middleware_path.rindex('.')
            except ValueError:
                raise exceptions.ImproperlyConfigured('%s isn\'t a middleware module' % middleware_path)
            mw_module, mw_classname = middleware_path[:dot], middleware_path[dot+1:]
            try:
                mod = import_module(mw_module)
            except ImportError, e:
                raise exceptions.ImproperlyConfigured('Error importing middleware %s: "%s"' % (mw_module, e))
            try:
                mw_class = getattr(mod, mw_classname)
            except AttributeError:
                raise exceptions.ImproperlyConfigured('Middleware module "%s" does not define a "%s" class' % (mw_module, mw_classname))

            try:
                mw_instance = mw_class()
            except exceptions.MiddlewareNotUsed:
                continue

            if hasattr(mw_instance, 'process_request'):
                request_middleware.append(mw_instance.process_request)
            if hasattr(mw_instance, 'process_view'):
                self._view_middleware.append(mw_instance.process_view)
            if hasattr(mw_instance, 'process_response'):
                self._response_middleware.insert(0, mw_instance.process_response)
            if hasattr(mw_instance, 'process_exception'):
                self._exception_middleware.insert(0, mw_instance.process_exception)

        # We only assign to this when initialization is complete as it is used
        # as a flag for initialization being complete.
        self._request_middleware = request_middleware

    def get_response(self, request):
        "Returns an HttpResponse object for the given HttpRequest"
        from google.appengine._internal.django.core import exceptions, urlresolvers
        from google.appengine._internal.django.conf import settings

        try:
            try:
                # Setup default url resolver for this thread.
                urlconf = settings.ROOT_URLCONF
                urlresolvers.set_urlconf(urlconf)
                resolver = urlresolvers.RegexURLResolver(r'^/', urlconf)

                # Apply request middleware
                for middleware_method in self._request_middleware:
                    response = middleware_method(request)
                    if response:
                        return response

                if hasattr(request, "urlconf"):
                    # Reset url resolver with a custom urlconf.
                    urlconf = request.urlconf
                    urlresolvers.set_urlconf(urlconf)
                    resolver = urlresolvers.RegexURLResolver(r'^/', urlconf)

                callback, callback_args, callback_kwargs = resolver.resolve(
                        request.path_info)

                # Apply view middleware
                for middleware_method in self._view_middleware:
                    response = middleware_method(request, callback, callback_args, callback_kwargs)
                    if response:
                        return response

                try:
                    response = callback(request, *callback_args, **callback_kwargs)
                except Exception, e:
                    # If the view raised an exception, run it through exception
                    # middleware, and if the exception middleware returns a
                    # response, use that. Otherwise, reraise the exception.
                    for middleware_method in self._exception_middleware:
                        response = middleware_method(request, e)
                        if response:
                            return response
                    raise

                # Complain if the view returned None (a common error).
                if response is None:
                    try:
                        view_name = callback.func_name # If it's a function
                    except AttributeError:
                        view_name = callback.__class__.__name__ + '.__call__' # If it's a class
                    raise ValueError("The view %s.%s didn't return an HttpResponse object." % (callback.__module__, view_name))

                return response
            except http.Http404, e:
                if settings.DEBUG:
                    from google.appengine._internal.django.views import debug
                    return debug.technical_404_response(request, e)
                else:
                    try:
                        callback, param_dict = resolver.resolve404()
                        return callback(request, **param_dict)
                    except:
                        try:
                            return self.handle_uncaught_exception(request, resolver, sys.exc_info())
                        finally:
                            receivers = signals.got_request_exception.send(sender=self.__class__, request=request)
            except exceptions.PermissionDenied:
                return http.HttpResponseForbidden('<h1>Permission denied</h1>')
            except SystemExit:
                # Allow sys.exit() to actually exit. See tickets #1023 and #4701
                raise
            except: # Handle everything else, including SuspiciousOperation, etc.
                # Get the exception info now, in case another exception is thrown later.
                receivers = signals.got_request_exception.send(sender=self.__class__, request=request)
                return self.handle_uncaught_exception(request, resolver, sys.exc_info())
        finally:
            # Reset URLconf for this thread on the way out for complete
            # isolation of request.urlconf
            urlresolvers.set_urlconf(None)

    def handle_uncaught_exception(self, request, resolver, exc_info):
        """
        Processing for any otherwise uncaught exceptions (those that will
        generate HTTP 500 responses). Can be overridden by subclasses who want
        customised 500 handling.

        Be *very* careful when overriding this because the error could be
        caused by anything, so assuming something like the database is always
        available would be an error.
        """
        from google.appengine._internal.django.conf import settings
        from google.appengine._internal.django.core.mail import mail_admins

        if settings.DEBUG_PROPAGATE_EXCEPTIONS:
            raise

        if settings.DEBUG:
            from google.appengine._internal.django.views import debug
            return debug.technical_500_response(request, *exc_info)

        # When DEBUG is False, send an error message to the admins.
        subject = 'Error (%s IP): %s' % ((request.META.get('REMOTE_ADDR') in settings.INTERNAL_IPS and 'internal' or 'EXTERNAL'), request.path)
        try:
            request_repr = repr(request)
        except:
            request_repr = "Request repr() unavailable"
        message = "%s\n\n%s" % (self._get_traceback(exc_info), request_repr)
        mail_admins(subject, message, fail_silently=True)
        # If Http500 handler is not installed, re-raise last exception
        if resolver.urlconf_module is None:
            raise exc_info[1], None, exc_info[2]
        # Return an HttpResponse that displays a friendly error message.
        callback, param_dict = resolver.resolve500()
        return callback(request, **param_dict)

    def _get_traceback(self, exc_info=None):
        "Helper function to return the traceback as a string"
        import traceback
        return '\n'.join(traceback.format_exception(*(exc_info or sys.exc_info())))

    def apply_response_fixes(self, request, response):
        """
        Applies each of the functions in self.response_fixes to the request and
        response, modifying the response in the process. Returns the new
        response.
        """
        for func in self.response_fixes:
            response = func(request, response)
        return response

def get_script_name(environ):
    """
    Returns the equivalent of the HTTP request's SCRIPT_NAME environment
    variable. If Apache mod_rewrite has been used, returns what would have been
    the script name prior to any rewriting (so it's the script name as seen
    from the client's perspective), unless DJANGO_USE_POST_REWRITE is set (to
    anything).
    """
    from google.appengine._internal.django.conf import settings
    if settings.FORCE_SCRIPT_NAME is not None:
        return force_unicode(settings.FORCE_SCRIPT_NAME)

    # If Apache's mod_rewrite had a whack at the URL, Apache set either
    # SCRIPT_URL or REDIRECT_URL to the full resource URL before applying any
    # rewrites. Unfortunately not every Web server (lighttpd!) passes this
    # information through all the time, so FORCE_SCRIPT_NAME, above, is still
    # needed.
    script_url = environ.get('SCRIPT_URL', u'')
    if not script_url:
        script_url = environ.get('REDIRECT_URL', u'')
    if script_url:
        return force_unicode(script_url[:-len(environ.get('PATH_INFO', ''))])
    return force_unicode(environ.get('SCRIPT_NAME', u''))

